1. Field of the Invention
The invention relates to a force transducer and, more particularly, to a load cell having a spring body that deforms under action of a force or load to be measured, and a sensor including two separate sensor parts attached at different locations of the spring body and that generates a sensor signal dependent on the position of the sensor parts relative to one another.
2. Description of the Invention
In general, force transducers and load cells in particular are measuring transducers that convert a force or load acting on them into an electrical analog or digital measurement signal. In this case, a usually metal spring body is elastically deformed in a manner proportional to the applied load or force and the resultant deformation of the spring body or of particular parts of the spring is detected using suitable sensors. Changes in length on bent parts are usually detected using strain gages. Alternatively, changes in distance resulting from the deformation may be capacitively detected. The sensor means, such as strain gages or capacitor surfaces, are directly attached to the spring body.
EP 0 534 270 A1 or DE 10 2008 019 115 A1 disclose a force transducer or a load cell having a capacitive. The capacitive sensor has two electrodes (i.e., capacitor plates) that engage in one another in a comb-like manner and are attached to different parts of the spring body. The load cell operates according to the deflection method, i.e., a change in the force or load to be measured gives rise to a change in the sensor signal, the deflection of which is processed further.
DE 37 16 615 C2 discloses a weighing system operating according to the compensation method, so-called compensation scales, in which a counterforce is exerted on a movably guided load sensor using an electrodynamic drive. In this case, the position of the load sensor is detected using a capacitive sensor and the current flowing through a coil of the electrodynamic drive is controlled based on the sensor signal such that the load sensor is kept in a load-independent equilibrium position. The coil current is then a measure of the load.
Micromechanically produced sensors, such as Micro-Electro-Mechanical Systems (MEMS) sensors, have increasingly broad fields of application. WO 02/103369 A1 shows, for example, a capacitively operating MEMS acceleration sensor having two interengaging comb electrodes (i.e., capacitor plates), one of which is arranged on a rigid base body and the other of which is arranged on a carrier that is suspended in an oscillating manner from the base body.
Depending on the application and size of the force or load to be measured, the spring bodies used in force transducers or load cells have different designs and dimensions. Since only very small deformations or movements generally and only smaller deformations or movements can be linearly detected using micromechanically produced sensors on account of the small size of the latter, there is the problem of selecting suitable MEMS sensors for spring bodies of different size and design or, from the point of view of the MEMS sensors, of finding suitable locations at which they can be arranged on the spring body. In this case, production tolerances of the spring body also play a greater role than in conventional sensors. In addition, a compromise must be found between measurement range and measurement sensitivity.